Fluid treatment



April 1965 WILLIAM Kwo-wE CHEN ETAL. 3,179,583

April 1965 WlLLIAM Kwo-wE` CHEN ETAL 3,l79,583

FLUID TREATMENT u 3 Sheets-Sheet 3 Filed July 26, 1960 INVENTOR. WILLlAMKWO-WEI CHEN MILTON SHELDON MlNTZ ATTORN EY United States Patent Ofiice3,179,583 Pa'zented Apr. 20, 1965 3,179,583 FLUID TREATMENT WilliamKwo-Wei Chen and Milton Sheldon Mintz, Stamford, Conn., assignors to TheAmerican Machine and Foundry Company, a corperation of New Jersey FiledJuly 26, 1960, Ser. No. 45,415 1 Claim. (Cl. 204-301) This inventionrelates in general to the treatment of fluids in electrode chambers,and, more particularly, to the acidification of electrodialysis stacks.

In the treatment of natural brines and other solutions byelectrodialysis, the base produced at the cathode and at polarizedinterfaces between the surface of a membrane and the solution causestroublesome precipitation if some means is not provided to counteractit. Methods have been proposed which utilize the acid produced at theanode to counteract the formation of a base elsewhere in the stack.Since the quantity of acid produced electrolytically at the anode cannever eXceed the quantity of the base produced within the stack, theseprocedures provide no Safety factor and slight changes in the brine orsolution characteristics of the fluid being treated may readily upsetthe delicate electrochemical balance. For this reason, it has been amore common ractice to add acid from an external source to theelectrodialysis stack. The major objection to this latter procedure isthe relatively high cost of the equipment required for introducing acidat the proper rate and pressure.

It is, therefore, an Object of this invention to provide a less costlymethod for the introduction of acid into an electrodialysis stack.

Another Object of this invention is to provide an electrodialysis stackwhich can be operated for longer periods of time without requiringservice due to precipitation within the stack.

An additional Object of this invention is to provide an inexpensiveapparatus which will circulate fluid from an external source through anelectrode chamber.

Yet another Object of this invention is to provide a simple apparatuswhich will add acid from an external source to the cathode chamber of anelectrodialysis stack.

Many other objects, advantages and features of invention reside in theparticular construction, combination and arrangement of parts involvedin the embodiment of the invention and its practice as will beunderstood from the following description and accompanying drawingwheren:

FIG. 1 is a perspective view of an electrodialysis stack with attachedacid feeding apparatus;

FIG. 2 is a side view of an electrodialysis stack with a central portionbroken away, with a small additional portion broken away in section toshow internal construction and with an attached acid feeding apparatus;

FIG. 3 is an exploded perspective view of the elements forming theelectrodialysis stack;

FIG. 4 is a Vertical longtudinal enlarged section through a fragment ofone end of the electrodialysis stack and the attached acid feedingapparatus; and

FIG. 5 is a perspective view of a fragment of one end of a gasket and anadjacent membrane.

Referrng to the drawing in detail, FIGS. 1, 2 and 4 show an assembledelectrodialysis stack generally designated by the nurneral 29. The stack29 is clamped between two end plates 30 and 31, which may be steel orother rigid material, by tightening the bolts 32 and drawing the endplates together. Heavicr blocks of electrical insulating material 33 and34 may be placed inside the end plates 30 and 31 so that the bolts 32are disposed beyond the center of the stack 29 and electricallyinsulated from it. The end plate 30 and the block 33 have the cathodechamber intake and exhaust pipes 36 and 35 fixed into them. The endplate 30 also receives the product stream pipe 39 and the concentratestream pipe 40. In a like manner, the end plate 31 receives two intakestream pipes 41 and 42 and the anode chamber intake and eXhaust pipes 37and 38. Referring now to FIG. 3, the pipes 35, 36, 37, 38, 39, 40, 41and 42 lead to fluid flow apertures 64, 63, 73, 74, 61, 62, 70 and 71respectively, which are formed in the elements compris ing the stack 29.These fluid fiow apertures in the stack elements form manifold passageswithin the stack 29.

Referring now to FIG. 5, a gasket 50 is an elongated rectangle in itsexternal shape with a central rectangular cutout portion 52. Pars offluid flow apertures 45 and 46 at each end of the gasket 50 formmanifold passages. Communicating from one of these fluid flow apertures45 or 46 to the cutout chamber 52 are the small passages 47. Thus eachend of the gasket 50 contains small passages 47 communicating withoppositely disposed fluid flow apertures to form hydraulic Connections.A membrane 48 lies next to each side of each gasket 50. The membranes 48contain manifold apertures corresponding to those formed in the gaskets50.

FIGS. 3 and 4 show the arranged elements of an electrodialysis stack. Asteel plate 31 or other reinforcement member, a plastic block 34 and aninsulating sheet contain the two fluid intake apertures 61 and 62 andalso the anode chamber intake and exhaust apertures 73 and 74. Below theinsulating sheet 65 lies the gasket 66 having a central opening 77 whichprovides the anode chamber. This chamber may be from about 0.1 to about2.0 cm. thick. There are no internal passages formed within the gasket66 communicating with the manifold apertures 61 and 62 which it hasformed in one end. The anode chamber 77 contains the anode 67 which maybe of platinum foil or other suitable material. An electrical connection68 extends from this anode to be connected to a suitable current source.The connection 68 may also be seen in FIGS. 1 and 2.

After the gasket 66, there is placed a sheet 69 of a porous non-wovenmaterial which is sufliciently porous to allow either anions or cationsto pass while it resists the passage and attack of chlorine or otherdegradation agents generated at an electrode. This sheet 69 may be madeof any porous, relatively inert material. Following the sheet 69 thereare placed a number of layers each consisting of an anion permeablemembrane 48A, a gasket 50A, a cation permeable membrane 48K, and anothergasket StlB. It is to be noted that the gaskets 50A and 50B areidentical except that the gasket 50B is the same as gasket 50A in theinverted position. Thus fluid may flow from the intake manifolds formedby the aligned fluid flow apertures 61 and 62 into alternate chambers52C or 521). In a like manner, fluid flows from these alternate chambersdesignated 52C or 52D into either a manifold formed by the fluid flowapertures 70 or a manifold formed by the fluid flow apertures 71.

As long a series of cells may be built up in this man ner as desred bystacking up the alternate layers of gaskets 50A and 50B with theinterspersed membranes 48A and 4331. At the other end of the stack, thelower end as seen in FIG. 3, there follows in reverse order anotherporous sheet 69 and another gasket 66 from about 0.1 to about 2.0 cm.thick which contains a cathode 72. Another insulating sheet 65, anotherplastic block 33 and another plate 30 follow; each containing the fluidflow apertures 70 and 71 and also the cathode chamber intake and eXhaustapertures 63 and 64. When the electrodes 67 and 72 are connected to adirect current source so that the electrode 67 is an anode and theelectrode 72 is a cathode, the cut out portions 52D in the gaskets 50Awill form diluting cells and the cut out portions SZC in the gaskets SGBwill form concentrating cells. Thus a solution entering the stackthrough the intake pipes 41 and 42 will emerge as a dilute and aconcentrate Stream.

Referring now to FIG. 4, a reservoir is connected to the electrodechamber 77 containing the cathode 72 by means of the pipes 35 and 36.EXtending upward from the reservoir 10 is the standpipe 11 which ventsthe reservoir 10 to the atmosphere through filter material 12.' The pipe36 communicates between the lower portion* of the reservoir 10 and thelower portion of the electrode compartment'77. The pipe 35 extends fromthe top of the electrode chamber '77 upwards at an angle until it entersthe reservoir 10. The reservoir 10 is filled with a suitable solution 14to a level which is higher than the top of the electrode compartment'77. Since a liquid will reach a State of equilibrium by seeking its ownlevel, the solution 14 will fill the electrode compartment 77. Thissolution 14 may be any suitable acid, or it may be water in which isplaced a premolded cake 25 of a suitable acid salt such as sodiumbisulfate to form a saturated solution. If a solid cake of an acid salt,or if acid salt in a loose form, is packed in the reservoir 10, the topcover 15 of the reservoir 10 may be made removable so that the reservoirmay be more easily charged. If a liquid acid solution is used, it may beeasily poured into the reservoir 10 through the standpipe 11.

When the electrodialysis stack is in operation, bubbles 26 will beliberated at the cathode 72. These bubbles will rise within the solutionin the electrode compartment and they will continue to move upwardthrough the pipe 35. Since the density of the Combined fiuid and bubblemxture in the electrode compartment '77 and the pipe 35 will be lessthan that of the solution alone, the relatively more dense fiuid 14within the reservoir 10 will force some of the fiuid 14 and the risingbubbles within the electrode chamber 77 and the pipe 35 to percolate.out of the pipe 35 and back into the reservoir 10.

The gasses which are liberated at the cathode 72 pass upward throughpipe 35 into the reservoir 16 in the bubbles 20 and then escape from thereservoir 10 through the standpipe 11. In this manner a recirculation offiuid between the reservoir 10 and the cathode chamber 77 is mainta'nedas long as the electrodialysis stack is operating. This is a vapour liftdevice which depends on the passage of gas through liquid in a confinedchannel.

The top of pipe 35 need not be placed above the level of the solution 14in the container 10 as shown in FIG. 4. If pipe 35 terminates below thelevel of the solution 14, the rate of circulation will increase as thebubbles 20 will not have to raise the fluid to a given head beforecirculation starts, but the bubbles will only have to overcome thehydraulic resistance of the recirculation path. In any case, the pipe'35 leading from the top of the electrode compartment to the reservoir10 must extend generally upward or a vapour lock may result. A pocket ofthe released gas in bubble form which was trapped by a downwardextension of pipe 35 could interrupt the recirculation flow. Thisapparatus requires little attention and will automatically operatesimultaneously with the electrodialysis stack without requiring themanipulation of any valves or other controls. The reservoir 10 may bemade of suicient capacity so that an electrodialysis stack may operatefor a very long period of time before the acid or acid salt solution isused up in treating bases formed at the cathode. Further, if an anionpermeable membrane 48A is placed adjacent to the cathode '72, watertransferred by electroendosmosis will be directed out of the cathodeconpartment. However, an equilibrium water content will be mantained asnormal osmotic water transfer takes place back into the cathodecompartment by virtue of its high acid or Salt concentration.

If the electrodialysis stack operates in the manner that has beendescribed, the anode may be washed by means of water directed into pipe37 which will then ex-haust through pipe 33. However, if it is desiredto reverse the stack periodically electrically (for example, everyquarter hour or perhaps every two or three hours), the pipes 37 and 38may also be connected to the reservoir 10 in the same manner as are thepipes 35 and 36. In this case, either anion permeable membranes tA orcation permeable membranes 48K would be placed adjacent to bothelectrode compartments so that water transfer out of one electrodecompartment by electroendosmosis would tend to be balanccd by watertransferred into the other electrode compartment by means ofelectroendosmosis. Water transferred into an electrode compartment byelectroendosmosis would be carried upwards by bubbles into container 10While water transferred out of an electrode compartment byelectroendosmosis would tend to balance such an accumula tion of water.This feature of the invention would allow electrical reversal to be madeat longer intervals as the fluid level would not be changing in thereservoir 10.

If a separate reservoir were connected to each electrode chamber of anelectrodialysis stack which was periodically electrically reversed, thecapacity of each reservoir would have to be sufiicient to contain wateradded by electroendosmosis to one of the two chambers before electricalreversal. To extend the period of operation before electrical reversalbecame necessary, an overfiow could be provided in each reservoir todrain off excess fiuid.

While one particular electrodialysis stack structure has been shownhaving parallel flow through it, this :invention rnay be used ineleotrodialysis apparatus regardless of its construction or flowpattern. This invention may also be used in .other applications whereinit is desired to circulate fiuid from a reservoir through an electrodecontaining compartment. r

What is claimed is;

in electrodialysis apparatus having ion selec tive permeable membranesdefining alternating concentrating and diluting cells, between a pair ofend electrode chambers, a cathode :in one electrode chamber and an anodein the other electrode chamber, a direct current source connected tosaid elcctrodes, and means for fiowing a concentrate stream and adi-luting Stream through said concentrating and diluting cells, theimprovernent comprising a vented reservoir for an acid to be circulatedcontinuously through the cathode electrode chamber, a first conduitextending upwardly from the topof the cathode electrode chamber to saidreservoir, and a second conduit extending from said .reservoir to thelower end of said cathode electrode chamber, whereby bubbles of gasliberated at the cathode during operation of the apparatus create avapor lift to induce circulation of acid continuously between thereservoir and the cathode electrode chamber.

Refercnces Cited by the Examiner UNITED STATES PATENTS 1,986,920 1/35Cross 204-301 2,180,663 11/39 Delavenna 204-234 2,204,506 6/ 40MacDouga-ll 204-272 2,796,395 6/57 Roberts 2G4-237 2,848,403 8/58Rosenberg 204- 2,863,813 12/58 Juda 204-30l 3,003,940 10/61 Mason204-18Q IOHN H. MACK, Primary Examner.

MURRAY TILLMAN, Exam'ner.

